module/cpufreq: fix domain cpus.

- Use related_cpus rather than affected_cpus inside get_domain_cpus to
  return all cpus in the domain (including those online). This changes
  the behavior, but old behavior was almost certainly wrong as the
  method is memoized, and so the result should not be affected by
  hotplug.
- Add a non-memoized get_affected_cpus() which implements the old
  behavior.
diff --git a/devlib/module/cpufreq.py b/devlib/module/cpufreq.py
index e18d95b..c4bc14f 100644
--- a/devlib/module/cpufreq.py
+++ b/devlib/module/cpufreq.py
@@ -412,6 +412,17 @@
         """
         return self.target._execute_util('cpufreq_trace_all_frequencies', as_root=True)
 
+    def get_affected_cpus(self, cpu):
+        """
+        Get the CPUs that share a frequency domain with the given CPU
+        """
+        if isinstance(cpu, int):
+            cpu = 'cpu{}'.format(cpu)
+
+        sysfile = '/sys/devices/system/cpu/{}/cpufreq/affected_cpus'.format(cpu)
+
+        return [int(c) for c in self.target.read_value(sysfile).split()]
+
     @memoized
     def get_domain_cpus(self, cpu):
         """
@@ -420,7 +431,7 @@
         if isinstance(cpu, int):
             cpu = 'cpu{}'.format(cpu)
 
-        sysfile = '/sys/devices/system/cpu/{}/cpufreq/affected_cpus'.format(cpu)
+        sysfile = '/sys/devices/system/cpu/{}/cpufreq/related_cpus'.format(cpu)
 
         return [int(c) for c in self.target.read_value(sysfile).split()]